mkdir /zzz
mount /dev/sda3 /zzz
mount -t proc none /zzz/proc
mount -o bind /dev /zzz/dev
chroot /zzz /bin/bash
grub
find /boot/grub/stage1
root (hd0,2)
setup (hd0)

For /boot/grub/menu.lst, a minimal config would be

default Linux
timeout 2
title Linux
root (hd0,2)
kernel=/boot/vmlinuz root=/dev/sda3 ro

also check /zzz/etc/fstab.